Russian and US presidents are widely expected to discuss North Korean situation and Syrian conflict.
US president issued plea a day before the two world leaders will meet for the first time at the G20 summit.
15,000 police deployed to monitor thousands of protesters marching on streets during two-day summit.
It will be their first face-to-face meeting together.
Trump, Putin and Erdogan will be greeted by an army of up to 100,000 demonstrators in Hamburg on Saturday.
Boris Nemtsov was shot dead as he walked home with his girlfriend in February 2015.
Trump and Putin look set to meet at the G20 summit for the first time.
Angela Merkel is the most trusted leader from one of the four most powerful countries.
The US Treasury Department has expanded sanctions against more than three dozen Russian individuals and firms.
If Brazil's top prosecutor agrees, Congress will decide whether Temer should be investigated.
European Court of Human Rights says law is discriminatory and encourages homophobia.
Australian defence ministry says it has suspended the aerial campaign as a 'precautionary measure'.
Moscow urges US and other parties to respect Syria's territorial sovereignty.
Comey testified last week that he leaked a memo detailing a conversation with US President Donald Trump.
In a strong message, the congressional body voted 97 - 2 to pass the amendment.
The show's host Stephen Colbert took the director to task over what was described as a 'fawning' interview with the Russian leader.
Mattis said Putin had decided to be "strategic competitor" rather than a close ally to the US.
Baton-wielding riot police broke up anti-government demonstrations in several cities across Russia and arrested scores of protesters.
Putin says Russia is seeking to improve ties, but is frustrated by Washington's "imperialist mentality."
The opposition leader has been detained at his home, but his wife says the rallies will go ahead.
The German Foreign Ministry confirmed that the first man arrived on Tuesday.
Stone's own interview with the Russian leader has been described as a "wildly irresponsible love letter."